Blue-yellow color vision defects result from mutations in the OPN1SW gene. These changes lead to an absence of L or M cones or to the production of abnormal opsin pigments in these cones that affect red-green color vision. Genetic changes involving the OPN1LW or OPN1MW gene cause red-green color vision defects. The opsin made from the OPN1SW gene is more sensitive to light in the blue/violet part of the visible spectrum (short-wavelength light), and cones with this pigment are called short-wavelength-sensitive or S cones. The opsin made from the OPN1MW gene is more sensitive to light in the middle of the visible spectrum (yellow/green light), and cones with this pigment are called middle-wavelength-sensitive or M cones. The opsin made from the OPN1LW gene is more sensitive to light in the yellow/orange part of the visible spectrum (long-wavelength light), and cones with this pigment are called long-wavelength-sensitive or L cones. The OPN1LW, OPN1MW, and OPN1SW genes provide instructions for making the three opsin pigments in cones. The brain combines input from all three types of cones to produce normal color vision. There are three types of cones, each containing a specific pigment (a photopigment called an opsin) that is most sensitive to particular wavelengths of light. Cones provide vision in bright light, including color vision. The retina contains two types of light receptor cells, called rods and cones, that transmit visual signals from the eye to the brain. They are found in the retina, which is the light-sensitive tissue at the back of the eye. The proteins produced from these genes play essential roles in color vision. Mutations in the OPN1LW, OPN1MW, and OPN1SW genes cause the forms of color vision deficiency described above. Blue cone monochromacy is sometimes considered to be a form of achromatopsia, a disorder characterized by a partial or total lack of color vision with other vision problems. Affected individuals have additional vision problems, which can include increased sensitivity to light (photophobia), involuntary back-and-forth eye movements (nystagmus), and nearsightedness ( myopia ). These two forms of color vision deficiency disrupt color perception but do not affect the sharpness of vision (visual acuity).Ī less common and more severe form of color vision deficiency called blue cone monochromacy causes very poor visual acuity and severely reduced color vision. Blue-yellow color vision defects (also called tritan defects), which are rarer, cause problems with differentiating shades of blue and green and cause difficulty distinguishing dark blue from black. Affected individuals have trouble distinguishing between some shades of red, yellow, and green. Red-green color vision defects are the most common form of color vision deficiency. Color vision deficiency (sometimes called color blindness) represents a group of conditions that affect the perception of color.
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